Sulforaphane and ophthalmic diseases

Abstract Sulforaphane (SFN) is an organosulfur compound categorized as an isothiocyanate (ITC), primarily extracted from cruciferous vegetables like broccoli and cabbage. The molecular formula of sulforaphane (SFN) is C6H11NOS2. SFN is generated by the hydrolysis of glucoraphanin (GRP) through the enzyme myrosinase, showing notable properties including anti‐diabetic, anti‐inflammatory, antimicrobial, anti‐angiogenic, and anticancer attributes. Ongoing clinical trials are investigating its potential in diseases such as cancer, neurodegenerative diseases, diabetes‐related complications, chronic kidney disease, cardiovascular disease, and liver diseases. Several animal carcinogenesis models and cell culture models have shown it to be a very effective chemopreventive agent, and the protective effects of SFN in ophthalmic diseases have been linked to multiple mechanisms. In murine models of diabetic retinopathy and age‐related macular degeneration, SFN delays retinal photoreceptor cell degeneration through the Nrf2 antioxidative pathway, NF‐κB pathway, AMPK pathway, and Txnip/mTOR pathway. In rabbit models of keratoconus and cataract, SFN has been shown to protect corneal and lens epithelial cells from oxidative stress injury by activating the Keap1‐Nrf2‐ARE pathway and the Nrf‐2/HO‐1 antioxidant pathway. Oral delivery or intraperitoneal injection at varying concentrations are the primary strategies for SFN intake in current preclinical studies. Challenges remain in the application of SFN in eye disorders due to its weak solubility in water and limited bioavailability because of the presence of blood–ocular barrier systems. This review comprehensively outlines recent research on SFN, elucidates its mechanisms of action, and discusses potential therapeutic benefits for eye disorders such as age‐related macular degeneration (AMD), diabetic retinopathy (DR), cataracts, and other ophthalmic diseases, while also indicating directions for future clinical research to achieve efficient SFN treatment for ophthalmic diseases.


| INTRODUC TI ON
People worldwide are increasingly focusing on their vegetable consumption to maintain good health and prevent diseases.
This review comprehensively presents recent research on SFN, elucidates its mechanism of action, and discusses potential therapeutic benefits for eye disorders such as age-related macular degeneration (AMD), diabetic retinopathy (DR), cataracts, and other ophthalmic diseases.Structured searches were conducted on prominent online databases, including PubMed, Embase, and Cochrane Library databases.
Broad search terms were employed to identify relevant research, including sulforaphane, eye diseases, age-related macular degeneration, F I G U R E 1 The metabolism of sulforaphane (SFN): with different environmental temperatures, PH, and coenzyme factors, the glucoraphanin (GRP) could be hydrolyzed by the myrosinase into epithionitrile, isothiocyanates, thiocyanate, and nitrile.As one of the most reactive degradation products, isothiocyanate (ITC) can transform into SFN, which will be further metabolized through the mercapturic acid pathway to synthesize LSF-N-Acetyl-Lcysteine (LSF-NAC) and LSF-L-cysteine (LSF-cys).diabetic retinopathy, and cataract.Extracted studies primarily focused on in vivo preclinical models of SFN.The subheadings in the review are listed as biological activity for SFN, mechanism of SFN, SFN and ophthalmic diseases, ongoing and completed clinical trials on SFN, safety and toxicity of SFN, future perspectives, and conclusion.

| B I OLOG I C AL AC TIVIT Y FOR S FN
SFN exhibits weak solubility in water but demonstrates solubility in organic solvents like methanol, ethanol, dimethyl sulfoxide, and ethyl acetate.It typically appears as a yellow or colorless liquid at room temperature.Moreover, the molecule is susceptible to disintegration at high temperatures, given its relatively low melting point of 74.6°C (Table 1).In human administration, SFN can be delivered either directly in its active form or as GRP.Upon oral administration, SFN is often absorbed from the intestine, displaying lower bioavailability, a shorter half-life, and a significant first-pass effect.
Furthermore, SFN interacts with glutathione (GSH) and glutathione-S-transferase within cells, initiating the mercapturic acid pathway.
Furthermore, clinical investigations have highlighted the influence of material sources on SFN bioavailability in the human body.For instance, peak plasma concentrations of SFN were seven times higher in subjects consuming fresh broccoli sprouts compared to broccoli supplements, with corresponding urine excretion five times higher.These findings underscore the substantially higher bioavailability of SFN when derived from whole food sources, facilitated by the presence of myrosinase in fresh broccoli sprouts (Clarke, Hsu, Riedl, et al., 2011;Fahey et al., 2015).

| MECHANIS M OF S FN
The ITC (-N=C=S) group features an electrophilic carbon, imparting high activity to SFN compared to the biologically inert phytochemical protostar GRP.Recent research has elucidated SFN's potential as an anti-diabetic, anti-inflammatory, antimicrobial, anti-angiogenic, anticancer, and antioxidant agent.The primary pharmacophore in SFN, the ITC group, is believed to induce cell apoptosis, phase G2/M cell cycle arrest, inhibition of phase-I (carcinogen-activating) enzyme, and stimulation of phase-II (carcinogen-detoxifying) enzyme.Moreover, SFN has the ability to scavenge free radicals and bind to a number of oxidizing agents, including hydroxyl, peroxide, and superoxide radicals.Previous research has demonstrated that the antioxidative function of SFN is associated with the activation of nuclear factor-erythroid 2-related factor 2 (Nrf2), a key regulator found in numerous organs (Zhou et al., 2022).Nrf2 is widely recognized as the "master redox switch" and "activator of cellular defense mechanisms".Typically, Nrf2 resides in a complex with Kelch-like ECH-associated protein 1 (Keap-1) and is tethered to cytosolic actin filaments.Upon detection of external stimuli by Keap-1, Nrf2 dissociates from Keap-1, translocating to the nucleus to upregulate the expression of target genes by binding to antioxidant response elements (AREs) in their upstream promoter regions (Dinkova-Kostova et al., 2005;Houghton, 2019;Prestera et al., 1993).At the molecular level, SFN interacts with protein targets such as the mammalian target of rapamycin (mTOR), acting as both a potent Nrf2 activator and mTOR inhibitor, thus playing a critical role in cellular homeostasis regulation (Russo et al., 2018;Zhang et al., 2021).The properties of Nrf2 make it a promising novel drug target with potential applications across a wide range of conditions.

| Anti-diabetic activity
Diabetes mellitus (DM) is a chronic, noncommunicable disease that is characterized by hyperglycemia and insulin resistance.The progression of macrovascular, microvascular, and neuropathic changes in DM leads to complications such as kidney disease, blindness, and amputations,  affecting over 8% of the global population (Tönnies et al., 2019).
Current treatments for reducing glycemic levels primarily involve insulin injections and oral medications, both of which have the potential to decrease mortality and enhance the quality of life for diabetes patients.However, there are limited reports on DM prevention, and existing treatments simply focus on slowing down the disease's progression.Recent research by Wang et al. (2022) has demonstrated that SFN might activate Nrf2 to prevent diabetes-induced oxidative stress and diabetic cardiomyopathy (Gu et al., 2017;Xin et al., 2018).Studies conducted by Li et al. (2020) et al., 2017;Bahadoran et al., 2012).In summary, SFN would be an ideal choice for the treatment of type 2 diabetes.

| Anti-inflammatory activity
The nuclear factor kappa-light-chain-enhancer of activated B cells On the other hand, SFN upregulates the expression of Nrf2 and heme oxygenase-1 (HO-1), potentially increasing the production of anti-inflammatory cytokines like IL-4 and IL-10 (Subedi et al., 2019).
Recent research by Yang et al. (2022) indicated that SFN can downregulate the expression of IL-4Rα, TNFRI, and TNFRII.Consequently, decreased levels of phosphorylation were observed in MAPKs, STAT6, and IκBα, ultimately alleviating allergic inflammatory keratoconjunctivitis (Yang et al., 2022).Additionally, sulforaphane exhibits the potential to inhibit peritoneal cell recruitment and IL-1β secretion in acute gout, reverse the resistance of Bacillus anthracis spore infection, and mitigate inflammatory injury to renal tubular epithelial cells.These properties position SFN as a promising treatment for chronic inflammatory diseases (Kim & Park, 2016;Liu et al., 2020;Mazarakis et al., 2020).

| Antimicrobial activity
According to previous research on infectivity, SFN has shown promise in limiting the growth of bacterial pathogens, particularly Helicobacter pylori.SFN induces bacterial mortality by disrupting cell membrane integrity and inhibiting enzymes responsible for maintaining redox balance and bacterial metabolism (Romeo et al., 2018).
This action of antibacterial has been specifically described.

| Anti-angiogenic activity
Angiogenesis is a multifaceted process that includes the release of angiogenic factors, incorporation between angiogenic factors and endothelial cell receptors, activation, migration, and proliferation of endothelial cells (ECs), remodulation of the extracellular matrix, and the formation of tubes (Carmeliet & Jain, 2000).Angiogenic factors and interactions between endothelial cells and the perivascular matrix regulate angiogenesis.Nowadays, the anti-angiogenic effect of SFN has been widely investigated.Nishikawa et al. (2010) conducted an in vitro model of angiogenic ECs by isolating human umbilical vein endothelial cells (HUVECs).They discovered that SFN could induce apoptosis, consequently inhibiting the proliferation ability of ECs.Moreover, it was found that combining SFN with an inhibitor of autophagy could enhance the effect on ECs (Nishikawa et al., 2010).To further explore the anti-angiogenic potentials of SFN, Liu, Atkinson, et al. (2017) additionally used in vitro models involving HUVECs and human hepatocellular carcinoma cells (HepG2).Their findings indicated that SFN reduced the vitality, migration, and tube formation of HUVEC cells.

| Anticancer activity
The anticancer properties of SFN have been extensively explored in recent years, demonstrating its potential to effectively inhibit the viability, proliferation, migration, malignancy, and epithelial-to-mesenchymal transition in cancer cells.SFN has shown its anti-cancer actions in the skin, blood, breast, colon, prostate, and pancreas.Notably, SFN has been found to block stem cell formation and suppress the Wnt/βcatenin pathway signaling, both of which are crucial in the treatment of triple-negative breast cancer (Arzi et al., 2022;Li et al., 2010).In a recent study by Zhang et al. (2022), SFN and its two isomers, R-SFN and S-SFN, significantly reduced migration and invasion induced by TGF-1 in breast cancer cells.They also reported that SFN inhibited the formation of actin stress fibers by downregulating RAF/MEK/ERK pathway signaling, ultimately reducing breast cancer cell metastasis (Zhang et al., 2022).Additionally, Aumeeruddy and Mahomoodally (2019) observed that a combination of three phytochemicals-SFN, piperine, and thymoquinone-could enhance therapeutic efficacy against breast cancer compared to individual treatments.SFN has been observed to induce apoptosis in hepatocellular carcinoma cells, causing morphological changes such as cell contraction, blistering, chromatin condensation, and nuclear fragmentation (Wu et al., 2020).Furthermore, SFN reduced the viability and telomerase activity of hepatocellular carcinoma Hep3B cells by activating ROS-dependent pathway signaling and reducing microtubule polymerization (Moon et al., 2010;Pocasap et al., 2018).
Research by Ren et al. (2017) indicated that SFN improved the radiosensitivity of hepatocellular carcinoma by inhibiting NF-κB pathway signaling, which plays an essential role in the development of liver cancer.
They also found that, SFN suppressed the expression of downstream genes in the NF-kB pathway in hepatocellular carcinoma cells (Ren et al., 2017).In addition, the molecular pathway of antitumor activity has also been reported as a novel therapy target (Rafiei et al., 2020).Rafiei et al. (2020) discovered that SFN has excellent miRNA modulatory capability, with the ability to either up-or down-regulate miRNA expression in the promotion or repression of cancer.

| Anti-oxidant activity
As an essential factor in the antioxidant defense system, the expression of Nrf2 significantly increased after SFN treatment, which could activate cellular antioxidant enzymes and protect against oxidative stress.The Nrf2-ARE signal pathway plays a pivotal role in upregulating protective genes and proteins associated with antioxidant properties, encompassing both direct antioxidant enzymes (like catalase, superoxide dismutase, and GSH peroxidase) and indirect antioxidant enzymes (like GSH generation enzymes and Phase-2 detoxification enzymes) (de Figueiredo et al., 2015).In addition, research conducted by Lv, Meng, et al. (2020) revealed that the antioxidative properties and SFN levels of broccoli vary among cultivars, seeds, and sprouts.Interestingly, they found that broccoli sprouts exhibited greater antioxidant capability than the original seeds, despite lower SFN levels in the sprouts compared to the seeds (Table 2) (Lv, Meng, et al., 2020).
TA B L E 2 Biological activity and mechanism of action of SFN.However, SFN may be able to reduce the oxidative stress caused by PM2.5 and subsequently increase the viability of ARPE-19 cells.
Meanwhile, the pre-treatment with SNF could significantly reverse the pro-apoptotic changes, such as reduced protein levels of Bax, cleaved caspase-3, as well as cytosolic cytochrome c, and increased levels of Bcl-2 (Sim et al., 2021).Taken together, these results suggest that the antioxidant SFN, especially when exposed to PM2.5, may be a valuable and potential therapeutic agent for AMD.

| Diabetic retinopathy
Diabetic retinopathy (DR), one of the most severe complications of diabetes, has emerged as a leading cause of blindness, significantly impacting the quality of life for many diabetic patients (Antonetti et al., 2012).An early histopathologic change associated with DR is the loss of pericytes, often occurring without noticeable symptoms.However, once visual symptoms manifest, the progression of DR can become irreversible and potentially lead to blindness (Ting et al., 2016).Several distinct changes characterize DR, including the development of microaneurysms, thickening of the retinal basement membrane, and increased permeability of the retinal vessels.
These changes are attributed to oxidative stress, the accumulation of advanced glycation end products (AGEs), inflammasome activation, and inflammation (Lai et al., 2017;Shruthi et

| Cataract
Cataract, characterized by lens opacification, is effectively treated through surgical intervention, leading to rapid recovery post-surgery (Asbell et al., 2005).However, approximately 20% of patients may experience complications known as posterior capsule opacification (PCO), resulting from residual lens epithelial cell adhesion to the anterior capsule after surgery.PCO is typically treated with a neodymium:YAG laser, but this approach carries some complications and risks (Wormstone et al., 2021).Recent research has revealed that SFN exhibits a hormetic effect, contributing to both cytotoxicity and cytoprotection.On the one hand, SFN is believed to have cytotoxic actions.Once the concentrations reach 10 μM and above, they may significantly interfere with lens cell wound healing, which could eventually prevent PCO.Huynh et al. (2021), using models of the central anterior epithelium and the human lens epithelial cell line FHL124, found that SFN depletes GSH in lens cells by downregulating GSH reductase activity.This accumulation of oxidative stress and ROS promotes progression, including endoplasmic reticulum stress (ERS), mitochondrial dysfunction, autophagy, and DNA damage, ultimately resulting in lens cell death (Huynh et al., 2021).Liu, Smith, et al. (2017) also suggested that SFN could retard the growth, migration, and viability of lens epithelial cells.Concurrently, SFN-induced autophagy was regulated by MAPK signaling and MEK signaling (Liu, Smith, et al., 2017).On the other hand, SFN has been reported to upregulate the activity of Nrf2/ARE/Prdx6 peroxiredoxin and activate cellular antioxidant enzymes, thereby protecting aging lens epithelial cells.Additionally, SFN enhances the survivability of lens epithelial cells and reactivates Nrf2 in aged and dysregulated cells (Calabrese & Kozumbo, 2021).In lens epithelial cells exposed to hydrogen peroxide, Liu et al. (2013) found that SFN could reduce DNA damage, transparency loss, and cell death.They also demonstrated that SFN could protect lens cells from oxidative stress by activating Keap1-Nrf2-ARE pathway (Liu et al., 2013).Furthermore, Varma et al. (2013) suggested that SFN increased the transcription of thioredoxin reductase in lens cells, eventually reducing oxidative stress.In conclusion, SFN exhibits a concentration threshold for its opposing actions, with the level determining cell viability and death.
In lens epithelial cells, SFN demonstrates cytoprotective effects at lower concentrations, making it a potential tool for repairing and reversing cataracts.In contrary, at concentrations of 10 μM and above, SFN displays cytotoxicity and may serve as a potential therapy for PCO.

| Other eye-related diseases
Several studies also reported the promising role of SFN in other VKC due to its efficacy in suppressing late-phase allergic inflammation (Yang et al., 2022).In the study of keratoconus, Liu and Yan (2018) found that SFN, through activation of the Nrf-2/HO-1 antioxidant pathway, could protect rabbit corneas from oxidative stress.This protection led to lowered keratometry and increased central cornea thickness, ultimately inhibiting the progression of keratoconus (Liu & Yan, 2018).Moreover, Kang and Yu (2017) suggested that continuous treatment with SFN could significantly inhibit GRP78/BiP expression in the ER of the rd10 retina, indicating that SFN could reduce ERS and subsequently reduce photoreceptor apoptosis.This protective effect demonstrated in a mouse model of retinitis pigmentosa highlights SFN as a potential drug to ameliorate retinal degeneration (Kang & Yu, 2017).Ambrecht et al. (2015) initially reported the protective effect of SFN on retinal ischemic injury.SFN was shown to significantly alleviate ischemia-induced retinal dysfunction and the inner retinal layers' attenuation compared to vehicle-treated mice.Besides, they demonstrated that SFN therapy given at a dose of 25 mg/kg/day for 5 days can have neuroprotective effects on both the initial ischemia injury and the ensuing reperfusion injury.The neuroprotective effects were attributed to the activation of the antioxidant Nrf2/HO-1 pathway.SFN could be a potential treatment for diseases causing retinal ischemia, such as diabetic retinopathy and retinal vascular occlusions (Ambrecht et al., 2015;Pan et al., 2014).In Fuchs endothelial corneal dystrophy (FECD), Ziaei et al. (2013) demonstrated the effectiveness of SFN.By enhancing Nrf2-ARE pathway signaling, SFN was able to reduce corneal endothelial cell apoptosis in FECD (Ziaei et al., 2013).
Additionally, studies by Kong et al. (2007) showed that SFN could retard photoreceptor degeneration in tubby mice.Intraperitoneal injection with SFN significantly elevated Nrf2, Trx, and TrxR levels in the retina, providing protection to photoreceptor cells in tubby mice and potentially preventing inherited neurological disorders, including retinal dystrophic syndromes and retinitis pigmentosa (Table 3) (Kong et al., 2007).

| ONGOING AND COMPLE TED CLINI C AL TRIAL S ON S FN
Prior to its introduction to the market, extensive clinical trials were conducted to ensure the safety and efficacy of herbal medicines containing SFN. exploring suitable surfactant types and dosages, and determining the optimal drug-to-lipid ratio.
Secondly, delivering drugs to the eye through blood-ocular barrier systems remains a major challenge.While systemic medication administration is one approach to treating ocular diseases, drug transfer to the retina via circulating blood is primarily regulated by two blood-ocular barrier systems: the blood-retinal barrier and the blood-aqueous barrier (Tomi & Hosoya, 2010).Thus far, only a few

ACK N OWLED G M ENTS
Not applicable.

CO N FLI C T O F I NTE R E S T S TATE M E NT
The authors declare no conflicts of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data sharing is not applicable to this article as no new data were created or analyzed in this study.

E TH I C S S TATEM ENT
This study does not involve any human or animal testing.

I N FO R M E D CO N S E NT
Written informed consent was obtained from all study participants.

(
NF-κB) and Nrf2 pathways serve as crucial mediators for SFN's anti-inflammatory effects.During the inflammatory process, SFN effectively regulates mitogen-activated protein kinase (MAPK) signaling, a key player in modulating both pro-and anti-inflammatory responses in LPS-activated microglia.Studies by Subedi et al. (2019) demonstrated significant reductions in MAPK phosphorylation levels in microglial cells following pre-and post-treatment with SFN.On one hand, SFN diminishes c-Jun N-terminal kinase (JNK) phosphorylation levels, subsequently decreasing NF-κB and activator protein-1 (AP-1) signaling.This reduction leads to decreased transcription of proinflammatory cytokines, including IL-6, IL-1β, and TNFα, as well as inflammatory mediators such as COX-2, iNOS, PGE, and NO.
demonstrated that SFN enhanced the inhibition of MEK/ERK and PI3K/AKT pathways, which can synergistically increase forkhead box O (FOXO) transcriptional activity; it can also inhibit cell migration and capillary tube formation.In conclusion, SFN inhibits angiogenesis through the activation of FOXO transcription factors and the inhibition of STAT3/HIF-1α/VEGF signaling.

4
| S FN AND OPHTHALMI C D IS E A S E S4.1 | Age-related macular degenerationAccording to the World Health Organization, AMD has been listed in the top 10 eye diseases and has become a leading cause of blindness among elderly people.AMD, a degenerative macular retinal disease, severely impairs vision in affected elderly adults.While various risk factors contribute to AMD, oxidative stress and choroidal vascular dysfunction play critical roles in its pathogenesis(Kwa et al., 2019;Ruan et al., 2021).Current treatments primarily focus on vascular endothelial growth factor inhibitors, and SFN has emerged as a promising treatment for AMD.The model of mouse retinal degeneration has been established and applied to many clinical trials.Age-related changes in Nrf2 expression and function are observed in retinal pigment epithelial (RPE) cells of old mice(Sachdeva et al., 2014).Qi et al. (2022) evaluated whether the lack of the transcription factor constrains the therapeutic efficacy of SFN against retinal degeneration.They suggested that SFN could retain the function of the cone, but in mice with reduced Nrf2 function, the efficiency may be limited(Qi et al., 2022).The pathophysiology of inflammatory injury to RPE cells has been investigated using microarray analysis.Ye et al. (2013) indicated that, after treatment with SFN, significant changes were observed in the transcription of 69 genes in human retinal pigment epithelium 19 (ARPE-19) cells.Several processes, including anti-apoptosis, anti-oxidation, and cell growth regulation, were associated with these cells.SFN improved the antioxidative ability of RPE 19 cells by upregulating antioxidative genes (including quinone oxidoreductase [NQO1], sulfiredoxin1 homolog [SRXN1], thioredoxin 1 [Trx1], and glutamate-cysteine ligase modifier subunit [GCLM]), and downregulating inflammatory response genes (such as thioredoxin interacting protein [TXNIP], chemokine [C-C motif] ligand 2 [CCL2], and bradykinin receptor B1 [BDKRB1]).Moreover, through Nrf2 antioxidative pathways, SFN may modulate the promoters of the antioxidant response elements (NQO1, GCLM, and Trx1) (Ye et al., 2013).Furthermore, Song et al. (2022) showed that SFN prevents lipopolysaccharide (LPS)-induced inflammatory damage to RPE cells by inhibiting the PWRN2/NF-kB pathway.They suggested that SFN blocked NF-kB activation and downregulated PWRN2 in a concentration-dependent manner.Conversely, NF-kB upregulation or PWRN2 overexpression reduced the anti-inflammatory effects of SFN (Song et al., 2022).The RPE cell layer plays an important role in protecting retinal photoreceptors from oxidative stress.Furthermore, it has been indicated that declining protective capacity may play a significant role in AMD development.By enhancing Trx expression in the mouse retina, Tanito et al. (2005) demonstrated that SFN could reduce retinal light damage.Additionally, intraperitoneal and oral administration of SFN upregulates the expression of the Trx gene in RPE cells by antioxidant response element (ARE) and affords cytoprotection against lightinduced RPE and photoreceptor cell damage in mice.Although SFN plays an indirect role in antioxidants, it could induce the transcription of phase II genes, thereby exerting the antioxidant effect.Bypromoting the expression of Trx and phase II enzymes, SFN may be a useful preventative measure for retinal illnesses caused by photooxidative stress, which may worsen the severity and progression of AMD(Tanito et al., 2005).Gao and Talalay (2004) also demonstrated that SFN prevented photooxidative damage to RPE cells by promoting the expression of phase 2 genes.Pre-conditioning RPE cells with SFN, acting as an inducer of phase 2 genes, demonstrated a considerable level of protection.The degree of protection was consistent with the capacity of inducers to enhance cytoprotective GSH levels and NAD(P)H activities(Gao & Talalay, 2004).Moreover, polyunsaturated fatty acids have been shown to increase the incidence of AMD, while oxidized lipids may contribute to the innate immunological dysfunction associated with oxidative stress in AMD.According toKwa et al. (2019), L-sulforaphane (LSF) can protect adult pigment epithelial cells against oxidative damage by upregulating the gene expression of Glutathione-S-Transferase μ1 enzyme.They also indicated that retinal cells faced with oxidative damage and apoptosis risks should be pre-conditioned with LSF, which could retard AMD progression by regulating fatty acids and lipids involved in downstream pathways(Kwa et al., 2019).Recent research bySim et al. (2021) discovered the molecular basis of SNF's protective properties against particulate matter 2.5 (PM2.5)-inducedtoxic damage in ARPE-19 cells.Increased intracellular reactive oxygen species (ROS) levels or decreased antioxidant enzyme activity may result from exposure to PM2.5.Regarding AMD, the chronically excessive production and accumulation of ROS in RPE cells may be the primary cause of photoreceptor loss in the ultimate stage(Mao et al., 2014).
eye-related diseases.In vernal keratoconjunctivitis (VKC), Yang et al. (2022) demonstrated that SFN possesses anti-inflammatory and anti-allergenic characteristics.SFN was found to inhibit the expression of chemokines and adhesion molecules triggered by the costimulation of TNFα and IL-4 in human corneal fibroblasts.These included vascular cell adhesion molecule-1, thymus-and activationregulated chemokines, and eotaxin-1.The inhibitory effect was likely mediated by downregulating the expression of IL-4Rα, TNFRI, and TNFRII, and reducing phosphorylation levels in MAPKs, IκBα, and STAT6.Hence, SFN holds potential as a candidate for treating safe and efficient drug delivery systems have been reported, with nanotechnological formulations being commonly employed.Goldcoated iron oxide nanoparticles, albumin-based nanocarriers, and PCL-PEG-PCL copolymeric-based micelles have been explored to enhance SFN bioavailability in the eye(Kheiri Manjili et al., 2016,   2017;Naqvi et al., 2022).Further understanding of drug transporters expressed in the blood-retinal barrier and corneal epithelium may facilitate the development of more efficient medication delivery systems for ocular diseases(Jordán & Ruíz-Moreno, 2013).Moreover, as drug delivery systems advance, novel carriers capable of crossing blood-ocular barrier systems may be employed to treat eye conditions such as keratitis, AMD, and DR.Thirdly, optimizing the dose of SFN intake is imperative for future research.Previous clinical trials have typically administered SFNcontaining intervention drugs daily with a single dose.However, SFN's short elimination half-life in plasma, due to rapid metabolism by phase I and phase II drug metabolism enzymes, may restrict further absorption and distribution in the human body (Clarke, Hsu, Williams, et al., 2011).Consequently, the effective dose range of SFN remains unknown, with few clinical trials reporting dose F I G U R E 2 The mechanism and future development of SFN for eye diseases [By Figdraw.]:SFN can be applied in treating various ophthalmic diseases like AMD, DR, cataract, PCO, VKC, keratoconus, retinal degeneration, retinal ischemic injury, FECD, and photoreceptor degeneration.The protective effects of SFN have been linked to mechanisms including the Nrf2 antioxidative pathway, NF-κB pathway, AMPK pathway, Txnip/mTOR pathway, and Nrf-2/HO-1 antioxidant pathway.responses to the drugs.Moreover, the doses used in the majority of animal experiments have exceeded the maximum dosage of SFN administered to humans.Thus, comprehensive dose-response studies of SFN are necessary to provide crucial information for establishing sensible SFN dose regimens to improve safety and efficiency in clinical translation.8| CON CLUS IONIn conclusion, other than anti-diabetic, anti-inflammatory, antimicrobial, anti-angiogenic, anticancer, and antioxidant activities, SFN can be used in ophthalmic diseases such as AMD, DR, cataract, PCO, VKC, keratoconus, retinal degeneration, retinal ischemic injury, FECD, and photoreceptor degeneration.Among them, a number of signal pathways, such as the Nrf2 antioxidative pathway, NF-κB pathway, AMPK pathway, Txnip/mTOR pathway, Keap1-Nrf2-ARE pathway, and Nrf-2/HO-1 antioxidant pathway, present significant protective effects.There are several limitations, such as poor solubility in water, low bioavailability, and the formidable blood-ocular barrier systems, SFN has yet to be clinically developed for the treatment of eye disorders.Nonetheless, owing to its numerous health benefits and advancements in novel drug delivery systems, the clinical application and promotion of SFN in ocular diseases hold promise for the future.Upon successful completion of rigorous clinical trials, future endeavors may focus on developing novel drug delivery systems tailored for ocular applications.Such advancements hold the potential to greatly facilitate the clinical translation of SFN, paving the way for its broader therapeutic use in ocular diseases (Figure2).AUTH O R CO NTR I B UTI O N SYichi Zhang: Data curation (equal); investigation (equal); writingoriginal draft (equal).Xiaojing Zhao: Data curation (equal); investigation (equal); writing -original draft (equal).Yang Liu: Supervision (equal); writing -review and editing (equal).Xiuxia Yang: Supervision (equal); writing -review and editing (equal).

PER S PEC TIVE S
(Alumkal et al., 2015;Zhang et al., 2020)ao et al., 2021)ical evidence concerning the therapeutic effects of SFN, sourced from the official clinical trial government website.SFN has been utilized as a dietary supplement for various disorders, including autism spectrum disorder, schizophrenia, lung cancer, prostate cancer, and chronic kidney disease.The majority of these trials have demonstrated considerable efficacy with SFN.Notably, a randomized, placebo-controlled, multidose trial was designed to evaluate SFN's efficacy in mitigating the long-term health risks associated with air pollution.The results revealed that SFN exhibited the abil-Zimmerman et al., 2021).Furthermore, observational studies have examined SFN's role as an adjunctive treatment for schizophrenia patients who were unresponsive to antipsychotic treatment(Central South University et al., 2018;Xiao et al., 2021).The effects and mechanism of action of SFN in ophthalmic diseases treatment.Recent clinical trials of SFN (ongoing and completed).Mangla et al., 2020).A few modest adverse effects, such as constipation, bloating, nausea, and headaches, have been reported in some patients(Alumkal et al., 2015;Zhang et al., 2020).
(Guerrero-Beltrán et al., 2010;Kerr et al., 2018)t al., 2021)e-related macular degeneration; DR, diabetic retinopathy; FECD, fuchs endothelial corneal dystrophy; RPE-19 cells, retinal pigment epithelium 19 cells; SFN, sulforaphane; VKC, vernal keratoconjunctivitis.TA B L E 4tolerance, with few apparent side effects noted apart from rare instances of insomnia, irritability, and intolerance of taste and smell (University ofMassachusetts, Worcester et al., 2015;Zimmerman et al., 2021).Moreover, pre-clinical experiments have indicated that SFN can potentiate the anticancer activity of drugs such as doxorubicin, tamoxifen, and cisplatin while mitigating off-target toxicity through multiple mechanisms(Calcabrini et al., 2020).For example, SFN could mitigate doxorubicin-induced cardiotoxicity by enhancing mitochondrial functions in the heart and alleviate cisplatin-induced nephrotoxicity by preventing changes in mitochondrial functionality in the kidney(Guerrero-Beltrán et al., 2010;Kerr et al., 2018).7 | FUTUREFirstly, enhancing SFN stability through formulation modifications is a critical direction for future studies.SFN exhibits weak solubility in water and displays lower bioavailability, a shorter halflife, and a significant first-pass effect, which limit its development.To enhance efficacy in treating ocular diseases, future development efforts may concentrate on selecting appropriate carrier materials,